Patch "pids: make task_tgid_nr_ns() safe" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

pids: make task_tgid_nr_ns() safe

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
pids-make-task_tgid_nr_ns-safe.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Oleg Nesterov <[email protected]>
Date: Mon, 21 Aug 2017 17:35:02 +0200
Subject: pids: make task_tgid_nr_ns() safe

From: Oleg Nesterov <[email protected]>

commit dd1c1f2f2028a7b851f701fc6a8ebe39dcb95e7c upstream.

This was reported many times, and this was even mentioned in commit 52ee2dfdd4f5 ("pids: refactor vnr/nr_ns helpers to make them safe") but somehow nobody bothered to fix the obvious problem: task_tgid_nr_ns() is not safe because task->group_leader points to nowhere after the exiting task passes exit_notify(), rcu_read_lock() can not help.

We really need to change __unhash_process() to nullify group_leader, parent, and real_parent, but this needs some cleanups. Until then we can turn task_tgid_nr_ns() into another user of __task_pid_nr_ns() and fix the problem.

---
 include/linux/pid.h   |    4 +++-
 include/linux/sched.h |   50 +++++++++++++++++++++++++++-----------------------
 kernel/pid.c          |   11 ++++-------
 3 files changed, 34 insertions(+), 31 deletions(-)

@@ -8,7 +8,9 @@ enum pid_type
 	PIDTYPE_PID,
 	PIDTYPE_PGID,
 	PIDTYPE_SID,
-	PIDTYPE_MAX
+	PIDTYPE_MAX,
+	/* only valid to __task_pid_nr_ns() */
+	__PIDTYPE_TGID
 };
 
 /*

@@ -526,8 +526,11 @@ pid_t __task_pid_nr_ns(struct task_struc
 	if (!ns)
 		ns = task_active_pid_ns(current);
 	if (likely(pid_alive(task))) {
-		if (type != PIDTYPE_PID)
+		if (type != PIDTYPE_PID) {
+			if (type == __PIDTYPE_TGID)
+				type = PIDTYPE_PID;
 			task = task->group_leader;
+		}
 		nr = pid_nr_ns(rcu_dereference(task->pids[type].pid), ns);
 	}
 	rcu_read_unlock();

@@ -536,12 +539,6 @@ pid_t __task_pid_nr_ns(struct task_struc
 }
 EXPORT_SYMBOL(__task_pid_nr_ns);
 
-pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
-{
-	return pid_nr_ns(task_tgid(tsk), ns);
-}
-EXPORT_SYMBOL(task_tgid_nr_ns);
-
 struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
 {
 	return ns_of_pid(task_pid(tsk));

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/pids-make-task_tgid_nr_ns-safe.patch queue-4.9/mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus.patch